Papers by Liliana Zaharia
Aerul şi apa, componente ale mediului, Mar 20, 2024
Flash Flood Forecasting Using Machine Learning Models: A Scientometric Analysis. Hydro-meteorolog... more Flash Flood Forecasting Using Machine Learning Models: A Scientometric Analysis. Hydro-meteorological hazards are a major issue in many regions of the world, including Romania. Among these, flash floods are the most frequent phenomena, generating significant annual socio-economic and environmental damages. In recent years, flash flood forecasting using machine learning algorithms has become an useful tool for data-based hydrologic modeling. Machine learning allows to create mathematical relationships between the river discharge and other climatic and physico-geographic parameters from the training dataset. This paper aims to perform a scientometric analysis using open-source programs, namely ScientoPyGui and VOSviewer. The expression 'flash flood forecasting AND machine learning' was searched in the Web of Science and Scopus databases. After merging and removing duplicates, 112 publications were retained for analysis. Their number has increased by 60% in the past three years (after 2021) with a trend towards a sub-branch of machine learning, namely deep learning. The spatial distribution of the papers showed that China is a global leader with 25% of the total. These findings highlight the increasing role of machine learning based models (particularly deep learning) in enhancing flash flood forecasting, a nonstructural measure for the flash flood risk mitigation.
Aerul şi apa, componente ale mediului, Mar 20, 2024
Spatial-temporal analysis of hydrological alerts and warnings for immediate phenomena in 2022 and... more Spatial-temporal analysis of hydrological alerts and warnings for immediate phenomena in 2022 and 2023 in Romania. The purpose of this paper is to highlight the spatial-temporal distribution of hydrological alert messages issued at the national level in the last two years, with a special focus on the accomplished percentage of the forecasted projected information. This paper used information from the database generated within National Institute of Hydrology and Water Management as part of the National Administration of Romanian Waters (NARW), which is the national authority to elaborate and distribute the warnings and alerts for immediate phenomena in Romania. The criteria for validating the hydrological warnings were based on the achievement of the predicted stream defense water levels, reaching precipitation thresholds or the existence/evidence of recorded damages. The actual analysis was carried out on the major hydrographic basins associated with the regional basin administrations. Three particular case studies were also analyzed, which spatially cover three distinct heterogeneously positioned regions, in order to have a better representativeness: the upper part of Someșului Mare river, the Bistrița, Moldova and Suceava rivers in Suceava county and the lower basin of Jiu River with its tributaries, as well as the Danube River on its sector within Iron Gates II Dam and its confluence with the Jiu River.
Dynamics of Islands and Danube River Channel Along Vedea-Călărași Sector (1856–2019): Hydrogeomorphological Approach
Springer eBooks, 2022
Variability of Nutrient Concentrations Along the Lower Danube River
Springer eBooks, 2022
Flow Variability of the Lower Danube River: An Up-to-Date Overview
Springer eBooks, 2022
At the crossroads of different fine sediment fingerprinting methods in the Jiu River Basin (SW Romania)
<p>Fine sediments in rivers hold the imprint of the lithological and geochemical fe... more <p>Fine sediments in rivers hold the imprint of the lithological and geochemical features of their origin areas and sometimes intermediate storage, as well as of the influence of human activities. This research addresses the issue of the heterogeneous sources and transfer paths of fine sediments in a medium-sized (10,080 sq.km), complex hydrographic basin, by combining several fingerprinting methods. The study basin belongs to the Jiu River (340 km length), which originates from the Meridional Carpathians and drains the pre-Carpathian hills and plains in SW Romania, before flowing into the Danube, to which it contributes with a considerable volume of suspended sediments (up to 20-25% during floods). A part of this fine sediment load is due to the coal industry in the upper and in the western half of the middle sectors, but also to socialist-time coal mining legacies from the alluvial deposits remobilized during floods, hence the particularity of the sediment chemical composition, which we explore in this research.</p> <p>Given the geological, geomorphological and anthropic complexity of Jiu River Basin and the different spatial and temporal scales involved in the production and transfer of fine sediments, their fingerprinting was attempted investigated through both conventional (heavy metals and lanthanides geochemistry) and alternative (colorimetry, image analysis and organic petrology) laboratory methods. In order to try to corroborate the different fingerprinting methods, alluvial samples were collected from: a) the Jiu riverbed and alluvial deposits on its banks, and b) the riverbeds of the major tributaries of the Jiu River (intermediate alluvial accumulations from both natural and man-disturbed geochemical sources).</p> <p>Different number of samples (from the total of 88) were used for each of the fingerprinting method. For the geochemical analyses, coal particles were separated by species (lignite and bituminous coal) by their density, while elemental analyses (for both heavy metals and rare earths) were performed by X-ray fluorescence (XRF) spectrometry (SR EN 15309: 2007) on the subsequent >2.8 g/l fraction. Based on their abundance, concentrations of the most relevant elements were retained for descriptive statistics. The main indicators (Zr/Si, Ti/Fe, Cu/Fe, Cu/S, Ca/Mg, Na/K, different Lanthanides/P ratios) were further correlated with the underlying lithology by means of nonparametric statistical tests. The color-based approach was conducted using a Minolta colorimeter and was further corroborated with the image analysis (performed by supervised classification and segmentation algorithms), to better distinguish the river sediments and coal samples in terms of the color shades and, thus, highlight the presence of coal. Finally, yet importantly, the organic petrology complemented the research by indicating the maceral composition of the coal-bearing bulk and alluvial samples and by improving our knowledge of the proportion of the two coal species present in the fine sediments.</p> <p>The laboratory analyses of the sediment samples combining several fingerprinting methods contributed to a better understanding of the hydro-sedimentary dynamics, providing new insight into fine sediment sources, their composition and transfer paths within Jiu River Basin.</p> <p><strong>Key words:</strong> coal, fine sediments dynamics, fingerprinting, laboratory analysis, Jiu River Basin</p>
Geochemical “testimonies” of fine sediments’ origins in a lithologically complex and coal mining disturbed Romanian river basin&#160
Assessing the Role of Snow Water Equivalent on the Spring Hydrological Regime of Șușișa River (Romania) Using SMA Hydrological Model in the Context of Climate Change
EGU General Assembly Conference Abstracts, Apr 1, 2018
Sediment sources in a complex river basin affected by coal mining: generating areas, processes and time periods. The case of Jiu river basin, Romania
EGU General Assembly Conference Abstracts, Apr 1, 2019
Atmosphere
The main goal of the present study is to identify the prevailing atmospheric circulation patterns... more The main goal of the present study is to identify the prevailing atmospheric circulation patterns (circulation types) that are associated with the occurrence of precipitation (both mean and extreme) over southern Romania. A daily circulation type calendar derived from an automatic and objective classification scheme is used in synergy with the daily precipitation time series from five weather stations in the study area for a sixty-year period (1961–2020). Both mean and extreme precipitation do not show statistically significant trends, except for the annual precipitation at Constanța, for the value with daily precipitation totals greater than the 95th percentile at Craiova and the number of days exceeding the 99th percentile at Buzău and Râmnicu -Vâlcea, where significant negative trends were noticed. Moreover, the precipitation trends were analyzed in relation to the atmospheric circulation types. Non-significant positive trends were observed for the precipitation amounts (annually...
Global NEST International Conference on Environmental Science & Technology
The variation of the total dissolved solids (TDS) in river water is highly dependent on the natur... more The variation of the total dissolved solids (TDS) in river water is highly dependent on the natural and anthropogenic features of the TDS source areas, namely the river basins upstream of the measurement points. Despite the significant theoretical knowledge on the factors governing the TDS variation in rivers’ waters, the quantification and modelling of the role of different environmental variables influencing the TDS has been less investigated. The objective of our work is to develop a methodology for estimating the contribution of the most significant natural and anthropic factors to the spatial variation of TDS, by integrating GIS and statistical tools. The methodology was applied on the Jiu River Basin (10,070 km2), located in SW Romania, covering different landforms (mountains, hills, plains) with diverse lithology, soils and land cover, as well as with various economic activities (one of which is coal mining). The study is based on TDS measurements on Jiu River and its main tr...
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Sediment connectivity assessment in a Romanian catchment affected by coal mining
EGU General Assembly Conference Abstracts, Apr 1, 2018
The assessment of river basin and flood management from early twentieth century to the present on the lower Siret River (Romania)
EGUGA, Apr 1, 2012
Estimation of climatic and anthropogenic contributions to streamflow change in southern Romania
Hydrological Sciences Journal
Understanding the effects of former river restoration actions is essential for gaining scientific... more Understanding the effects of former river restoration actions is essential for gaining scientific knowledge, feedback and guidance for future restoration projects. In this context, the objectives of our study are to analyze the surface-water variability and to assess the hydrological effects of restoration actions by means of riparian wetlands monitoring in the Lower Danube floodplain, in Romania. Independently from the monitored restoration project, we conducted an analysis of the Normalized Difference Water Index (NDWI) based on Landsat imagery (1984-2020) in the area of Gerai Marsh. We found that Gerai Marsh is connected occasionally to the Danube River, during large floods. The effects of restoration by reshaping local canals to (re)create the old Gerai Marsh were statistically detected in our study at the scale of 5 years postversus prerestoration and at p < 0.10. Our study confirmed the role of independent monitoring by standardized indicators from satellite remote sensing ...
Assessment of Restoration Effects in Riparian Wetlands using Satellite Imagery. Case Study on the Lower Danube River
Wetlands, 2022
The Lower Danube River
Twenty-five climate indices based on daily maximum and minimum temperature and precipitation at 1... more Twenty-five climate indices based on daily maximum and minimum temperature and precipitation at 15 meteorological stations were examined to investigate changes in temperature and precipitation extremes over the Yarlung Tsangpo River Basin (1970-2017). The trend-free prewhitening (TFPW) Mann-Kendall test and Pettitt's test were used to identify trends and abrupt changes in the time series, respectively. The results showed widespread significant changes in extreme temperature indices associated with warming, most of which experienced abrupt changes in the 1990s. Increases in daily minimum and maximum temperature were detected, and the magnitude of daily minimum temperature change was greater than that of the daily maximum temperature, revealing an obvious decrease in the diurnal temperature range. Warm days and nights became more frequent, whereas fewer cold days and nights occurred. The frequency of frost and icing days decreased, while summer days and growing season length increased. Moreover, cold spell length shortened, whereas warm spell length increased. Additionally, changes in the precipitation extreme indices exhibited much less spatial coherence than the temperature indices. Spatially, mixed patterns of stations with positive and negative trends were found, and few trends in the precipitation extreme indices at individual stations were statistically significant. Generally, precipitation extreme indices showed a tendency toward wetter conditions, and the contribution of extreme precipitation to total precipitation has increased. However, no significant regional trends and abrupt changes were detected in total precipitation or in the frequency and duration of precipitation extremes.
Hydrological Impacts of Climate Changes in Romania
Water Resources Management in Romania, 2019
This chapter provides a comprehensive synthesis of researches on hydro-climatic changes in Romani... more This chapter provides a comprehensive synthesis of researches on hydro-climatic changes in Romania and presents some original results on hydrological responses to climate changes in Valea Cerbului River basin (area of 26 km2) located in the Carpathian Mountains, based on the analysis of historical data and hydrological simulations. Although there are spatial differences, on the whole of Romania, after 1960, a general decreasing trend of the mean annual streamflow was detected. More or less significant changes in the annual flow regime were also noticed: upward trends in winter (related to the increase of the air temperature and liquid precipitations to the detriment of snowfall), downward trends in summer (induced by the general warming and increase of evaporation), and upward trends in the autumn flow. By 2050, the simulations under climate scenarios indicate a general decline of the mean multiannual discharges, significant increases of the discharges during winter and pronounced decreases in late summer and autumn. In Valea Cerbului River basin we investigated the changes in the magnitude and frequency of floods and low flows based on observational data, as well as the expected streamflow changes, as projected by simulations with WaSiM-Eth model (under B1, A2 and A1B climatic scenario, for the period 2001–2065 relative to 1961–2000 period). The simulations indicate a slight decrease in mean annual discharge (of 2% up to 6%) by 2065, an increase of mean monthly discharges from January to April, and a decline during May–December.
Inventorying, characterising and conserving on-farm ancient olive trees is a priority for safegua... more Inventorying, characterising and conserving on-farm ancient olive trees is a priority for safeguarding their genetic, natural and agricultural value and for protecting ancient genotypes threatened with extinction. In the "Taula del Sénia" (M-TdS) area (northeast Iberian Peninsula) a highly important cultural landscape has been preserved, in which the olive groves play an outstanding social and economic role: the ancient olive trees, sustained by many local farmers, constitute a living heritage and provide a clear example of High Nature Value (HNV). A total of 4,526 ancient productive olive trees, with a trunk circumference (PBH) larger than 3.5 m, were inventoried and their spatial localization and biometric measurements were collected. 41 olive trees have shown the highest category in monumentality (PBH>8.1 m). The outstanding trees might be 634-1082 years old. The endocarp morphology of a representative sample of the most ancient trees from this settlement resulted in 14 different profiles. The ancient trees genotyped, through eight simple sequence repeat (SSR) markers, revealed 43 SSR profiles. The use of SSR enabled us to verify that most of the trees (98%) belong to the local cv. 'Farga', a male sterile variety with a rare chlorotype, only a few trees corresponded with other local varieties, 'Morrut', 'Canetera' and 'Sevillenca', and ten hitherto unidentified genotypes were distinguished, some with chloroplast lineages different from the 'Farga' type. The M-TdS area holds a unique living and exploitable heritage with the highest concentration of ancient olive trees worldwide. On-farm conservation of this germplasm by the community of local growers is enabling preservation of this important source of genetic variation, potentially holding traits of resilience and adaptation to adverse soil and climatic conditions, demonstrated by the survival of these trees over the centuries. Farmers have undertaken initiatives to valorize the olive oil deriving from these M-TdS trees.
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Papers by Liliana Zaharia